For example, an image synthesis device disclosed by the following patent reference 1 receives image data showing images captured by a plurality of cameras mounted to a peripheral portion of a vehicle, and stores the image data in an input frame buffer. This image synthesis device refers to mapping data showing a correspondence between pixels in a bird's-eye view image viewed from an arbitrary point of view and pixels in each of the images captured by the cameras to generate a bird's-eye view image from the plurality of image data stored in the input frame buffer.
When generating a bird's-eye view image from the plurality of image data stored in the input frame buffer, the above-mentioned image synthesis device uses only the image data about an area in each of the images captured by the cameras but does not the image data about any area other than the above-mentioned area while storing all the image data showing the images captured by the cameras in the input frame buffer. Therefore, the input frame buffer disposed in the above-mentioned image synthesis device needs to have a large memory size.
An image synthesis device disclosed by the following patent reference 2 includes a special camera installed on an object and capable of changing an output area, and controls the output area of the camera according to the point of view of a bird's-eye view image (controls the range of an image captured by the camera) in order to be able to store only image data used for generation of a bird's-eye view image in an input frame buffer and reduce the memory size of the input frame buffer.